The invention is applicable to many camera designs, but has particular utility in low cost and single use cameras according to the preferred embodiment of the invention.
Single use cameras are assembled from relatively inexpensive components and sold with the film included. During manufacture, a film cartridge, typically in a standard 35 mm size and format, is positioned in the camera take-up chamber. Most of the film is then pulled from the cartridge, positioned across an exposure plane and prewound into the film supply chamber. In use, camera mechanisms advance the prewound film sequentially, one frame for each picture, from the supply chamber across the exposure plane and into the cartridge in the take up chamber. The advancing mechanism typically is a thumb wheel that rotates a spool inside the cartridge, winding the film onto the spool and thereby drawing the film into the cartridge.
Although simple in construction, single use cameras include suitable mechanisms for metering the film to position the individual frames properly in the exposure position. Perforations along an edge of the film engage and drive a sprocket wheel when the film is advanced. The sprocket wheel includes a notched metering cam that rotates with the sprocket, one revolution for each film frame. When a film frame is properly positioned for exposure, an arm on a film metering lever pivots into the notch. This pivotal motion moves another arm on the same lever into engagement with teeth around the periphery of the thumb wheel and thereby prevents further film advance.
An exposure is initiated by depressing an actuation button that releases a latch constraining a high energy striker. The striker drives a shutter blade to open an exposure aperture and expose the film. The striker also pivots the metering lever from the cam notch, releasing the thumb wheel. The thumb wheel is then free to advance the film for the next successive exposure, rotating the sprocket in engagement with the film perforations and resetting the high energy striker for the next exposure.
A single use camera of the type described above is disclosed, for example, in U.S. Pat. No. 5,235,366, issued Aug. 10, 1993.
Single use cameras offer numerous advantages for amateur photographers, including many features first introduced in more expensive camera models. At the same time, however, other features have proven difficult to adapt to the single use format. Motor driven automatic film winding and metering, for example, is not widely available in existing single use cameras.